The wind speed and direction aloft can be significantly different than what is experienced at the surface. A direct observation of wind shear can be done by noting differences in cloud movement. Surface friction slows the wind and causes a wind direction shift also at and near the surface. The movement of clouds aloft can be different than the wind direction experienced at the surface. The wind at the surface tends to be gustier but often with a lesser speed compared to the wind higher aloft. Less friction aloft both contributes to a smoother flowing wind and a stronger wind. Changes in wind speed and direction with height is known as wind shear. Clouds at different elevations can be moving in somewhat different directions. The speed of movement can be difficult to determine due to changes in depth perception with clouds of different heights. Direction of movement is easy to notice though. Strong wind shear is a contributing factor to severe weather. It may be noticed that clouds near the ground are moving from the south but clouds higher aloft are moving from the west. This indicates directional wind shear. A storm developing in this environment will twist with height due to the varying wind directions experienced with height as the cumulus develops vertically. In a severe weather situation, the winds will often increase with height. Influences from surface friction, the jet stream or a stronger pressure gradient can lead to stronger winds aloft. This type of shear can tilt a storm which results in a greater storm strength and longevity. On various days, note the clouds in the sky and classify the clouds as generally low level, middle and high clouds. Next note the direction the clouds are moving. An ideal situation would be to have some fair weather cumulus or stratus near the surface (low clouds), some clouds higher than these clouds (middle clouds) and cirrus type clouds above those (high clouds). Wind shear characteristics can be noticed by studying how these clouds are moving in relation to each other. |